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RE: need help/capacitors and AC



Original poster: "Scott Bogard" <teslas-intern@xxxxxxxxxxx>

Matthew,
I have never built an MMC, but I researched them, as I was going to build one. What is the voltage rating on your caps? 1200 seems like an awful lot of caps for an MMC (to me at least), especially considering you are using an NST, which probably has fairly low current (30, 60, or 90, mA). Re-run your calculations, {V=V1+V2+Vn..., and C=1/((1/C1)+(1/C2)+(1/Cn)...)} and if you get the same results, consider using different MMC caps (like the 942C rated at 1500 or 2000 volts). I would say, using the 2kV, you would need about 20 some, for a small 3 in. coil, and maybe a little more for a bigger coil, or a higher current supply (not 1200 capacitors). Plus remember, one can generally push the operating voltage of the caps a little beyond what they are rated (if you don't mind replacing one once in a while), but be careful, use peak voltage (15kV/.707) to calculate the necessary voltage rating of the capacitor!

Anyway, to answer your second question, I believe it works like this, as your frequency increases, your maximum current must go down (that is how it works with Maxwell caps, or so says the company that makes them).
Voltage breakdown is irrelevant (not really, but for your purposes it is).

To answer your third question, generally NSTs are 15kV from terminal to terminal (one is +7.5 kV, the other is -7.5 kV, and then they switch as the AC cycle progresses). Remember this is RMS voltage, use peak for calculating you capacitor voltage (RMS/.707). I hope this helps.
Scott Bogard.


From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: need help/capacitors and AC
Date: Wed, 02 May 2007 18:40:07 -0600

Original poster: "Matthew Boddicker" <shmerpleton_town@xxxxxxxxxxx>

This is Matthew Boddicker

I am currently designing a MMC, but I need the right capacitor for the job. I am going with cornell-dubilier caps, but my recent calculations said that I would require around 1200 caps for a MMC.

My question is how does a capacitor react to different frequencies of current? the cornell-dubilier web page says that the cap can handle 500Vac at 60Hz. if my circuit for my coil operates on a much higher frequency will I require a higher ac voltage rating or a lower one?

last question but equally relevant. My NST's output is 15,000 volts, is that the voltage between both output nodes or is 15,000 the voltage between one node and ground?

Thanks,
Matthew Boddicker

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